Authentication value for fluid ejection device

Abstract

A fluid ejection device includes a plurality of analog devices, and a storage element storing an authentication value including a plurality of bits, a first bit of the plurality of bits based on measured electrical characteristics of a first subset of the analog devices, and a second bit of the plurality of bits based on measured electrical characteristics of a second subset of the analog devices, the second subset different from the first subset.

What is claimed is: 
     
       1. A fluid ejection device, comprising:
 a plurality of analog devices; and 
 a storage element storing an authentication value including a plurality of bits, a first bit of the plurality of bits based on measured electrical characteristics of a first subset of the analog devices, and a second bit of the plurality of bits based on measured electrical characteristics of a second subset of the analog devices, the second subset different from the first subset. 
 
     
     
       2. The fluid ejection device of  claim 1 , wherein the electrical characteristics of at least some of the analog devices are measurable by a fluid ejection system, and wherein the authentication value is usable by the fluid ejection system to verify an authenticity of the fluid ejection device based on measured values of the at least some of the analog devices. 
     
     
       3. The fluid ejection device of  claim 1 , further comprising an electrical connection to connect to a host device, the electrical connection being connected to the storage element to communicate the authentication value to the host device, and being connected to the analog devices to facilitate measuring of the electrical characteristics of at least some of the analog devices by the host device. 
     
     
       4. The fluid ejection device of  claim 3 , further comprising an analog-to-digital converter coupled between the electrical connection and the analog devices to facilitate measuring the electrical characteristics of the at least some of the analog devices. 
     
     
       5. The fluid ejection device of  claim 1 , wherein the authentication value is generated based on comparisons of the measured electrical characteristics of respective subsets of the at least some of the analog devices. 
     
     
       6. The fluid ejection device of  claim 1 , wherein the authentication value stored in the storage element is encrypted. 
     
     
       7. The fluid ejection device of  claim 1 , wherein the authentication value comprises an encrypted version of a comparison value, the comparison value includes a plurality of bits, each bit to indicate a result of a comparison of the measured electrical characteristics of a respective subset of analog devices. 
     
     
       8. The fluid ejection device of  claim 1 , wherein the storage element further stores a measurement sequence key that indicates which analog devices were measured for a computation of the authentication value. 
     
     
       9. The fluid ejection device of  claim 1 , wherein the analog devices comprise resistors, and the measured electrical characteristics include resistances of the resistors. 
     
     
       10. The fluid ejection device of  claim 1 , further comprising a connector to communicate the authentication value to a fluid dispensing system as part of an authentication process performed by the fluid dispensing system to authenticate the fluid ejection device based on the authentication value. 
     
     
       11. A die comprising:
 a plurality of nozzles and a plurality of corresponding firing resistors; and 
 a storage element storing an authentication value including a plurality of bits, a first bit of the plurality of bits based on measured electrical characteristics of a first subset of the firing resistors, and a second bit of the plurality of bits based on measured electrical characteristics of a second subset of the firing resistors, the second subset different from the first subset. 
 
     
     
       12. The die of  claim 11 , further comprising an analog-to-digital converter to convert measured resistor values to digital values to facilitate measurement by a host device. 
     
     
       13. The die of  claim 11 , further comprising a connector to communicate the authentication value to a fluid dispensing system as part of authenticating the die by the fluid dispensing system. 
     
     
       14. The die of  claim 11 , wherein the storage element further stores a measurement sequence key that indicates which firing resistors were measured for a computation of the authentication value. 
     
     
       15. A die comprising:
 a plurality of analog devices; and 
 a storage element storing an authentication value including a plurality of bits, a first bit of the plurality of bits based on measured electrical characteristics of a first subset of the analog devices, and a second bit of the plurality of bits based on measured electrical characteristics of a second subset of the analog devices, the second subset different from the first subset. 
 
     
     
       16. The die of  claim 15 , wherein the authentication value is encrypted. 
     
     
       17. The die of  claim 16 , wherein encryption to provide the authentication value includes a conversion from a tristate number to a base-2 number.